Exhaust system for an engine

ABSTRACT

A valve for use in an engine exhaust conduit. The valve includes a base portion and a body portion extending from the base portion. The base portion is configured for pivotably mounting the valve within the engine exhaust conduit. The base portion defines a valve pivot axis. The valve is pivotable about the valve pivot axis during use. The body portion has an upstream side and a downstream side opposite the upstream side. The upstream side is exposed, during use, to fluid flow in the engine exhaust conduit. The body portion has a generally pointed shape defining a rounded tip at a location of the body portion furthest from the base portion in a length direction of the valve. The length direction of the valve is generally perpendicular to the valve pivot axis.

CROSS-REFERENCE

The present application claims priority to U.S. Provisional PatentApplication No. 62/678,922, filed on May 31, 2018 and U.S. ProvisionalPatent Application No. 62/783,576, filed on Dec. 21, 2018, the entiretyof both of which is incorporated herein by reference.

FIELD OF THE TECHNOLOGY

The present technology relates to engine exhaust systems.

BACKGROUND

For internal combustion engines, such as those used in snowmobiles, theefficiency of the combustion process can be increased by compressing theair entering the engine. This can be accomplished using a turbochargerconnected to the air intake and exhaust systems of the snowmobiles. Thecompression of the air by the turbocharger may be of particularimportance when the internal combustion engine is operated inenvironments where atmospheric pressure is low or when the air getsthinner, such as when the engine is operated at high altitudes.

The efficiency and the performance of some engines, especiallytwo-stroke engines, may however be hindered in certain circumstances bythe presence of a turbocharger because of an increased amount ofbackpressure caused by the turbocharger. Two-stroke engines tend to beespecially sensitive to non-optimal levels of backpressure.

There is thus a need for exhaust systems for internal combustion enginesthat can benefit from the addition of a turbocharger while overcomingsome of the previously known disadvantages of incorporating aturbocharger, including for example backpressure-related issues.

SUMMARY

It is an object of the present technology to ameliorate at least some ofthe inconveniences present in the prior art.

According to one aspect of the present technology, there is provided avalve for use in an engine exhaust conduit. The valve includes a baseportion and a body portion extending from the base portion. The baseportion is configured for pivotably mounting the valve within the engineexhaust conduit. The base portion defines a valve pivot axis. The valveis pivotable about the valve pivot axis during use. The body portion hasan upstream side and a downstream side opposite the upstream side. Theupstream side is exposed, during use, to fluid flow in the engineexhaust conduit. The body portion has a generally pointed shape defininga rounded tip at a location of the body portion furthest from the baseportion in a length direction of the valve. The length direction of thevalve is generally perpendicular to the valve pivot axis.

In some implementations, the body portion has a periphery including: twoopposite lengthwise edges extending from the base portion in a directiongenerally parallel to the length direction of the valve; a rounded edgedefined by the rounded tip; and two converging angular edges extendingbetween the two lengthwise edges and ends of the rounded edge. The twoangular edges converge toward each other as the two angular edges extendfrom the two lengthwise edges to the ends of the rounded edge.

In some implementations, each of the two angular edges is disposed at anangle between 10° and 45° inclusively relative to the length directionof the valve.

In some implementations, the body portion of the valve is symmetricalabout a plane bisecting the rounded tip. The plane is perpendicular tothe valve pivot axis.

In some implementations, the body portion has a width measured in adirection parallel to the valve pivot axis. The width of the bodyportion is largest adjacent the base portion and smallest at the roundedtip.

In some implementations, the valve has a length measured from the baseportion to the rounded tip in the length direction. A ratio of thelength of the valve over a maximal width of the body portion is greaterthan 1.

In some implementations, the ratio of the length of the valve over themaximal width of the body portion is between 1 and 2 inclusively.

In some implementations, the rounded tip has a tip radius. A ratio of amaximal width of the body portion over the tip radius is greater than 2.

In some implementations, the ratio of the maximal width of the bodyportion over the tip radius is between 2 and 6 exclusively.

In some implementations, the body portion includes a ridge disposed onthe upstream side. The ridge forms a closed shape.

In some implementations, the ridge forms a generally pentagonal shape.

In some implementations, the periphery of the body portion contours atleast a portion of the ridge.

In some implementations, the ridge includes: a base edge extendinggenerally parallel to the valve pivot axis, the base edge being disposednear the base portion of the valve; two outwardly-extending edges, eachoutwardly-extending edge extending from a corresponding end of the baseedge outwardly toward a corresponding one of the lengthwise edges of theperiphery of the base portion; and two inwardly-extending edges, eachinwardly-extending edge extending from an end of a corresponding one ofthe outwardly-extending edges. The inwardly-extending edges aregenerally parallel to the angular edges of the periphery of the bodyportion.

In some implementations, the ridge also includes rounded verticesincluding a distal rounded vertex that is furthest from the baseportion. The distal rounded vertex is generally concentric with therounded edge of the periphery of the body portion. Theinwardly-extending edges converge at the distal rounded vertex.

In some implementations, a cross-sectional profile of the ridge isgenerally trapezoidal.

In some implementations, the body portion includes a peripheral lipprotruding on the downstream side.

In some implementations, the base portion and the body portion are madeintegrally such that the valve is a single-piece component.

According to another aspect of the present technology, there is provideda turbocharger system for an internal combustion engine. Theturbocharger system includes a turbocharger for compressing and feedingair to the engine, and a bypass conduit in fluid communication with theengine and the turbocharger. The turbocharger has a turbine. The bypassconduit is configured to selectively direct exhaust gas to theturbocharger for operating the turbine or to bypass the turbine. Thebypass conduit includes a valve seat defining a valve opening. Theturbocharger system also includes a valve disposed in the bypass conduitfor controlling exhaust gas flow through the valve opening. The valveincludes a base portion and a body portion extending from the baseportion. The base portion is pivotably mounted within the bypass conduitat the valve seat. The base portion defines a valve pivot axis. Thevalve is pivotable about the valve pivot axis. The body portion has anupstream side and a downstream side opposite the upstream side. Theupstream side is exposed, during use, to exhaust gas flow in the bypassconduit. The body portion has a generally pointed shape defining arounded tip at a location of the body portion furthest from the baseportion in a length direction of the valve. The length direction of thevalve is generally perpendicular to the valve pivot axis. Theturbocharger system also includes a valve actuator and a controller incommunication with the valve actuator. The valve actuator is operativelyconnected to the base portion of the valve. The valve actuator isoperable to cause the valve to pivot about the valve pivot axis. Thecontroller controls operation of the valve actuator for controlling aposition of the valve.

In some implementations, the valve seat has a shape matching the shapeof the body portion of the valve.

In some implementations, the valve is movable by the valve actuatorbetween a plurality of positions including: an open position in whichexhaust gas flow through the valve opening is substantially unimpeded bythe valve; a closed position in which the valve fully closes the valveopening such that exhaust gas flow through the valve opening is cut offby the valve; and a plurality of intermediate positions between the openposition and the closed position.

In some implementations, the body portion comprises a ridge disposed onthe upstream side, the ridge forming a closed shape; and in the closedposition of the valve, the ridge sits against the valve seat.

In some implementations, the valve actuator is a servomotor.

In some implementations, the valve is oriented in the bypass conduitsuch that the rounded tip of the body portion is downstream of the baseportion of the valve.

In some implementations, the bypass conduit includes: a turbine outletportion for directing exhaust gas flow to the turbocharger, and a bypassoutlet portion for directing exhaust gas flow away from theturbocharger. The valve seat and the valve are disposed in the bypassoutlet portion to control exhaust gas flow into the bypass outletportion.

For purposes of this application, terms related to spatial orientationsuch as forwardly, rearward, upwardly, downwardly, left, and right, areas they would normally be understood by a driver of the snowmobilesitting thereon in a normal riding position. Terms related to spatialorientation when describing or referring to components or sub-assembliesof the snowmobile, separately from the snowmobile, such as a heatexchanger for example, should be understood as they would be understoodwhen these components or sub-assemblies are mounted to the snowmobile,unless specified otherwise in this application.

Implementations of the present technology each have at least one of theabove-mentioned object and/or aspects, but do not necessarily have allof them. It should be understood that some aspects of the presenttechnology that have resulted from attempting to attain theabove-mentioned object may not satisfy this object and/or may satisfyother objects not specifically recited herein. The explanations providedabove regarding the above terms take precedence over explanations ofthese terms that may be found in any one of the documents incorporatedherein by reference.

Additional and/or alternative features, aspects and advantages ofimplementations of the present technology will become apparent from thefollowing description, the accompanying drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present technology, as well as otheraspects and further features thereof, reference is made to the followingdescription which is to be used in conjunction with the accompanyingdrawings, where:

FIG. 1 is a left side elevation view of a snowmobile, with a portion ofa drive track represented;

FIG. 2 is a top, rear, right side perspective view of an engine, airintake system and exhaust system of the snowmobile of FIG. 1 ;

FIG. 3 is a front elevation view of the engine, air intake system andexhaust system of FIG. 2 ;

FIG. 4 is a cross-sectional view of the engine and some portions of theair intake system and the exhaust system of FIG. 2 ;

FIG. 5 is a top plan view of portions of the air intake system and theexhaust system of FIG. 2 ;

FIG. 6 is a schematic representation of a lubrication system of thesnowmobile of FIG. 1 ;

FIG. 7 is a schematic diagram of lubricating oil flow of the lubricationsystem of FIG. 6 ;

FIG. 8 is a schematic representation of the exhaust system of FIG. 2 ;

FIG. 9 is a close-up view of the portions of the air intake system andexhaust system of FIG. 5 ;

FIG. 10 is a right side elevation view of portions of the air intakesystem and the exhaust system of FIG. 2 ;

FIG. 11 is a close-up view of the portions of the air intake system andexhaust system of FIG. 10 ;

FIG. 12 is a front elevation view of a turbocharger, a bypass conduit,and an exhaust collector of the exhaust system of FIG. 2 ;

FIG. 13 is a perspective view of the bypass conduit of FIG. 12 , shownin isolation;

FIG. 14 is a cross-sectional view of the bypass conduit of FIG. 12 ,taken along line 14-14 of FIG. 13 , with a valve in a closed position;

FIG. 15 is the cross-sectional view of FIG. 14 , with the valve in anopen position;

FIG. 16 is the cross-sectional view of FIG. 14 , with the valve in anintermediate position;

FIG. 17 is a perspective view of portions of the turbocharger and thebypass conduit of FIG. 12 , with a portion of the top of the bypassconduit and the valve having been removed;

FIG. 18 is a top plan view of the turbocharger and bypass conduit ofFIG. 12 ;

FIG. 19 is a cross-sectional view of the turbocharger of FIG. 18 , takenalong line 19-19 of FIG. 18 ;

FIG. 20A is a left side elevation view of the exhaust collector of FIG.12 , shown in isolation;

FIG. 20B is a top, right side perspective view of the exhaust collectorof FIG. 20A;

FIG. 20C is a bottom plan view of the exhaust collector of FIG. 20A;

FIG. 21 is a flowchart illustrating a method, according to the presenttechnology, of controlling exhaust gas flow through the exhaust systemof FIG. 2 ;

FIG. 22 is a flowchart illustrating another method according to thepresent technology of controlling exhaust gas flow through the exhaustsystem of FIG. 2 ;

FIG. 23 is a flowchart illustrating another method according to thepresent technology of controlling exhaust gas flow through the exhaustsystem of FIG. 2 ;

FIG. 24 is a flowchart illustrating a method according to the presenttechnology for providing a fuel-air mixture to the engine of FIG. 2 ;

FIG. 25 is a cross-sectional view of the bypass conduit of FIG. 12 ,taken along line 25-25 of FIG. 13 , with the valve in the open position;

FIG. 26 is an elevation view of an upstream side of the valve of FIG. 14;

FIG. 27 is an elevation view of a downstream side of the valve of FIG.26 ;

FIG. 28 is a cross-sectional view of the valve of FIG. 26 , taken alongline 28-28 of FIG. 27 ;

FIG. 29 is a cross-sectional view of the valve of FIG. 26 , taken alongline 29-29 of FIG. 27 ; and

FIG. 30 is a chart representing a percentage mass flow through anopening as a function of a position of a valve;

FIG. 31 is a flowchart representing an illustrative scenario ofcontrolling exhaust gas flow through the exhaust system of FIG. 2 ;

FIG. 32 illustrates an example dataset for use in the illustrativescenario of FIG. 31 ;

FIG. 33 illustrates additional example datasets for use in theillustrative scenario of FIG. 31 ;

FIG. 34 illustrates example datasets used in the method of FIG. 24 ;

FIG. 35 is a partial cut-away view of an airbox of the air intake systemof FIG. 2 , with a portion of a left side of the airbox having beenremoved; and

FIG. 36 is a partial cut-away view of the airbox of FIG. 35 , with aportion of a rear side of the airbox having been removed.

It should be noted that the Figures may not be drawn to scale, exceptwhere otherwise noted.

DETAILED DESCRIPTION

The present technology is described herein with respect to a snowmobile10 having an internal combustion engine and two skis. However, it iscontemplated that some aspects of the present technology may apply toother types of vehicles such as, but not limited to, snowmobiles with asingle ski, road vehicles having two, three, or four wheels, off-roadvehicles, all-terrain vehicles, side-by-side vehicles, and personalwatercraft.

With reference to FIGS. 1 and 2 , a snowmobile 10 according to thepresent technology will be described. The snowmobile 10 includes aforward end 12 and a rearward end 14. The snowmobile 10 includes avehicle body in the form of a frame or chassis 16 which includes atunnel 18, an engine cradle portion 20, a front suspension module 22 andan upper structure 24.

An internal combustion engine 26 is carried in an engine compartmentdefined in part by the engine cradle portion 20 of the frame 16. A fueltank 28, supported above the tunnel 18, supplies fuel to the engine 26for its operation. The engine 26 receives air from an air intake system100. The engine 26 and the air intake system 100 are described in moredetail below.

An endless drive track 30 is positioned at the rear end 14 of thesnowmobile 10. The drive track 30 is disposed generally under the tunnel18, and is operatively connected to the engine 26 through a belttransmission system and a reduction drive. The endless drive track 30 isdriven to run about a rear suspension assembly 32 operatively connectedto the tunnel 18 for propulsion of the snowmobile 10. The endless drivetrack 30 has a plurality of lugs 31 extending from an outer surfacethereof to provide traction to the track 30.

The rear suspension assembly 32 includes drive sprockets 34, idlerwheels 36 and a pair of slide rails 38 in sliding contact with theendless drive track 30. The drive sprockets 34 are mounted on an axle 35and define a sprocket axis 34 a. The axle 35 is operatively connected toa crankshaft 126 (see FIG. 3 ) of the engine 26. The slide rails 38 areattached to the tunnel 18 by front and rear suspension arms 40 and shockabsorbers 42. It is contemplated that the snowmobile 10 could beprovided with a different implementation of a rear suspension assembly32 than the one shown herein.

A straddle seat 60 is positioned atop the fuel tank 28. A fuel tankfiller opening covered by a cap 92 is disposed on the upper surface ofthe fuel tank 28 in front of the seat 60. It is contemplated that thefuel tank filler opening could be disposed elsewhere on the fuel tank28. The seat 60 is adapted to accommodate a driver of the snowmobile 10.The seat 60 could also be configured to accommodate a passenger. Afootrest 64 is positioned on each side of the snowmobile 10 below theseat 60 to accommodate the driver's feet.

At the front end 12 of the snowmobile 10, fairings 66 enclose the engine26 and the belt transmission system, thereby providing an external shellthat not only protects the engine 26 and the transmission system, butcan also make the snowmobile 10 more aesthetically pleasing. Thefairings 66 include a hood 68 and one or more side panels which can beopened to allow access to the engine 26. A windshield 69 connected tothe fairings 66 acts as a wind screen to lessen the force of the air onthe rider while the snowmobile 10 is moving.

Two skis 70 positioned at the forward end 12 of the snowmobile 10 areattached to the front suspension module 22 of the frame 16 through afront suspension assembly 72. The front suspension module 22 isconnected to the front end of the engine cradle portion 20. The frontsuspension assembly 72 includes ski legs 74, supporting arms 76 and balljoints (not shown) for operatively connecting to the respective ski leg74, supporting arms 76 and a steering column 82 (schematicallyillustrated).

A steering assembly 80, including the steering column 82 and a handlebar84, is provided generally forward of the seat 60. The steering column 82is rotatably connected to the frame 16. The lower end of the steeringcolumn 82 is connected to the ski legs 74 via steering rods (not shown).The handlebar 84 is attached to the upper end of the steering column 82.The handlebar 84 is positioned in front of the seat 60. The handlebar 84is used to rotate the steering column 82, and thereby the skis 70, inorder to steer the snowmobile 10. A throttle operator 86 in the form ofa thumb-actuated throttle lever is mounted to the right side of thehandlebar 84. Other types of throttle operators, such as afinger-actuated throttle lever and a twist grip, are also contemplated.A brake actuator 88, in the form of a hand brake lever, is provided onthe left side of the handlebar 84 for braking the snowmobile 10 in aknown manner. It is contemplated that the windshield 69 could beconnected directly to the handlebar 84.

At the rear end of the snowmobile 10, a snow flap 94 extends downwardfrom the rear end of the tunnel 18. The snow flap 94 protects againstdirt and snow that can be projected upward from the drive track 30 whenthe snowmobile 10 is being propelled by the moving drive track 30. It iscontemplated that the snow flap 94 could be omitted.

The snowmobile 10 includes other components such as a display cluster,and the like. As it is believed that these components would be readilyrecognized by one of ordinary skill in the art, further explanation anddescription of these components will not be provided herein.

With additional reference to FIGS. 2 to 6 , the engine 26 and the airintake system 100 will be described in more detail. Air from theatmosphere flows through side apertures 113 defined in an upper portion25 of the upper structure 24 of the chassis 16. The air then flows intoa secondary airbox 110. The secondary airbox 110 is disposed above thefront suspension module 22. A generally Y-shaped conduit 118 (FIG. 2 )fluidly connects the secondary airbox 110, via a conduit portion 117, toan inlet 312 of an air compressor 310 (FIG. 5 ) disposed on the rightside of the engine 26. The conduit 118 further fluidly connects to aninlet 119 of a primary airbox 120 via a conduit portion 121. The primaryairbox 120 includes a bypass valve 123 (see FIGS. 35 and 36 )controlling air flow through the inlet 119 into the primary airbox 120.It is contemplated that the secondary airbox 110 could be omitted andthat air from the atmosphere could directly enter into the inlet 312and/or the inlet 119 of the primary airbox 120 without going through thesecondary airbox 110.

Air from the atmosphere, passing through the secondary airbox 110 andinto the air compressor 310 via the conduit 118 and inlet 312, iscompressed by the air compressor 310. The compressed air then flows outof the air compressor 310 through an outlet 314, into a conduit 316 andinto the primary air box 120. The primary airbox 120 is fluidlyconnected to the engine 26 via two air outlets 122 of the primary airbox120 (see also FIG. 10 ). The bypass valve 123 of the primary airbox 120is spring-loaded to a closed position, such that air is preferentiallyreceived from the air compressor 310 via the conduit 316. When the airpressure within the primary airbox 120 falls below a threshold value,for example when the engine 26 is rotating at a speed that requires moreair then is available in the primary airbox 120, the valve 123 opens toallow air from the atmosphere, via the secondary airbox 110, to enterthe primary airbox 120 directly.

In some situations, this can aid in obtaining optimal operation of theengine 26, especially when the turbocharger 300 is spooling and notsupplying the necessary air flow to the primary airbox 120 for the airbeing requested by the engine 26. As shown in FIG. 35 , valve 123includes a spring 125. The spring constant of spring 125 is chosen suchthat valve 123 will open and close at a predetermined pressure withinprimary airbox 120. Thus once opened, the bypass valve 123 willautomatically close when the airflow from the turbocharger 300 increasesthe pressure within the primary airbox 120 to the predeterminedpressure, and vice versa. The diameter of valve 123 is sized to allowfor a high flow capacity between the secondary and primary airboxes 110,120. This aids in ensuring optimal pressure within primary airbox 120and thus aids optimal engine performance in generally all situationseven if turbocharger 300 is not spooled. The conduit portion 117 and thebypass valve 123 also reduce the air flow travel distance between thesecondary airbox 110 and the primary airbox 120, when compared to theair flow travel distance through the conduit portion 121, theturbocharger 300 and the conduit 316. As such, depending on the airpressure within primary airbox 120, the airflow between the secondaryand primary airboxes 110, 120 has either a short airflow path or a longairflow path available. Inclusion of the bypass valve 123 in the primaryairbox 120 further allows the engine 26 to be operated in either aturbocharged mode or a naturally aspirated mode. Operation of the engine26, and corresponding operation of the turbocharger 300, in order tooperate in the two modes will be described in further detail below.

The engine 26 is an inline, two-cylinder, two-stroke, internalcombustion engine. The two cylinders of the engine 26 are oriented withtheir cylindrical axes disposed vertically. It is contemplated that theengine 26 could be configured differently. For example, the engine 26could have more or less than two cylinders, and the cylinders could bearranged in a V-configuration instead of in-line. It is contemplatedthat in some implementations the engine 26 could be a four-strokeinternal combustion engine, a carbureted engine, or any other suitableengine capable of propelling the snowmobile 10.

As shown in FIGS. 1, 2, and 4 , the engine 26 receives air from the airintake system 100, specifically the outlets 122 of the primary airbox120, via engine air inlets 27 defined in the rear portion of eachcylinder of the engine 26. Each air inlet 27 is connected to a throttlebody 37 of the air intake system 100. The throttle body 37 comprises athrottle valve 39 which rotates to regulate the amount of air flowingthrough the throttle body 37 into the corresponding cylinder of theengine 26. A throttle valve actuator (not shown) is operativelyconnected to the throttle valve 39 to change the position of thethrottle valve 39 and thereby adjust the opening of the throttle valve39 with operation of the throttle lever 86 on the handlebar 84. In thepresent implementation, the throttle valve actuator is a mechanicallinkage, although this is simply one non-limiting implementation. Theposition and the movement of the throttle valve 39 is monitored by athrottle valve position sensor 588 (schematically illustrated in FIG. 8) operatively connected to the throttle valve 39, described in moredetail below. It is also contemplated that the throttle valve actuatorcould be in the form of an electric motor. The electric motor couldchange the position of the throttle valve 39 based on input signalsreceived from an electronic control module (not shown) which in turnreceives inputs signals from a position sensor associated with thethrottle lever 86 on the handlebars 84. Further details regarding suchdrive-by wire throttle systems can be found in International PatentApplication No. PCT/US2013/048803 filed on Jun. 29, 2013, the entiretyof which is incorporated herein by reference.

The engine 26 receives fuel from the fuel tank 28 via Direct Injection(DI) injectors 41 and Multi Point Fuel Injection (MPFI) injectors 45(both shown in at least FIG. 4 ), having an opening in the cylinders.The fuel-air mixture in each of the left and right cylinders of theengine 26 is ignited by an ignition system including spark plugs 43(best seen in FIG. 2 ). Engine output power, torque and engine speed aredetermined in part by throttle opening and in part by the ignitiontiming, and also by various characteristics of the fuel-air mixture suchas its composition, temperature, pressure and the like. Methods ofcontrolling the fuel-air mixture, according to some implementations ofthe present technology, will be described in more detail below inreference to FIG. 24 .

Exhaust gases resulting from the combustion events of the combustionprocess are expelled from the engine 26 via an exhaust system 600 (FIG.5 ). As shown in FIG. 4 , an exhaust outlet 29 is defined in the frontportion of each cylinder of the engine 26. Each exhaust outlet 29 has anexhaust valve 129. The exhaust outlets 29 are fluidly connected to anexhaust manifold 33. The exhaust system 600 includes an exhaust pipe 202which is connected to the exhaust manifold 33 and extends forwardlytherefrom to direct the exhaust gases out of the engine 26.

A turbocharger 300 is operatively connected to the engine 26. Theturbocharger 300 compresses air and feeds it to the engine 26. As shownin FIGS. 6 and 12 , the turbocharger 300 has a housing 302 defining anair compressor 310 and an exhaust turbine 350. With additional referenceto FIG. 19 , the exhaust turbine 350 includes a turbine inlet 355 withan area 354, which is defined in turbochargers generally as thecross-sectional area of a volute 352 (measured at the tongue) of theexhaust turbine 350. The air compressor 310 includes a compressor wheeland is part of the air intake system 100. Intake air flowing past therotating compressor wheel is compressed thereby, as described above. Therotation of the compressor wheel is powered by a turbine wheel 351(FIGS. 19, 25 ) of the exhaust turbine 350, which is part of the exhaustsystem 600. The turbine wheel 351 is rotated by exhaust gases expelledfrom the engine 26 and directed to flow over the blades of the turbinewheel 351. It is contemplated that, in some implementations, the aircompressor 310 could be a supercharger, in which the compressor wheelwould be directly powered by the engine 26. The exhaust system 600 willbe described in greater detail below.

Referring to FIGS. 6 and 7 , the snowmobile 10 further includes alubrication system to provide lubricating oil to the engine 26 and tothe turbocharger 300. The engine 26 is fluidly connected to an oilreservoir 52 which supplies oil to the crankshaft 126 and the exhaustvalves 129 of the engine 26. The oil reservoir 52 is also fluidlyconnected to the turbocharger 300 to provide lubricating oil thereto.The turbocharger 300 is also fluidly connected to the engine 26, as willbe described further below.

A primary oil pump 54 is fastened to and fluidly connected to the oilreservoir 52. It is contemplated that the pump 54 and the oil reservoir52 could be differently connected together or could be disposedseparately in the snowmobile 10. The primary oil pump 54 pumps oil fromthe reservoir 52 to the engine 26 and the turbocharger 300. The primaryoil pump 54 includes four outlet ports for pumping out oil from the oilreservoir 52. Two outlet ports 53 supply oil to the crankshaft 126.Another outlet port 55 supplies oil to one of the exhaust valves 129.The fourth outlet port 57 supplies oil to the turbocharger 300.Depending on the implementation, it is contemplated that the primary oilpump 54 could include more or fewer outlet ports depending on specificdetails of the implementation.

A secondary oil pump 56 and an oil/vapor separator tank 59 are fluidlyconnected between the turbocharger 300 and the engine 26. The secondaryoil pump 56 receives oil that has passed through the turbocharger 300,and pumps that oil to the other exhaust valve 129. FIG. 7 illustratesthe flow directions of oil from the pumps 54, 56 and through theturbocharger 300 to the engine 26 via schematic diagram. It is furthernoted that in the present implementation, the turbocharger 300 is aball-bearing based turbocharger 300 which is dimensioned for low oilflow lubrication in order to provide efficient responsiveness. It iscontemplated that different types of turbochargers could be used indiffered implementations.

With this configuration, only one oil reservoir 52 is utilized forlubricating both the turbocharger 300 and the engine 26. It iscontemplated that the snowmobile 10 could also be arranged such that thesecondary oil pump 56 could be omitted. It is also contemplated that oilcould be circulated to the crankshaft 126, rather than the exhaustvalves 129, after having passed through the turbocharger 300.

With additional reference to FIGS. 8 to 19 , the exhaust system 600 willnow be described in further detail. The exhaust gas expelled from theengine 26 flows through the exhaust outlets 29, through the exhaustmanifold 33, and into the exhaust pipe 202, as is mentioned above. Theexhaust pipe 202, also known as a tuned pipe 202, is curved and has avarying diameter along its length. Other types of exhaust pipes 202 arecontemplated. As shown in FIG. 5 , the exhaust pipe 202 includes a pipeinlet 203 fluidly connected to the exhaust manifold 33 and a pipe outlet206 located at the end of the exhaust pipe 202. The exhaust pipe 202further has a divergent portion adjacent to the pipe inlet 203 and aconvergent portion adjacent the pipe outlet 206. The pipe outlet 206 ispositioned downstream from the pipe inlet 203.

The exhaust system 600 also includes a bypass conduit 620 to direct theflow of the exhaust gas to either bypass the turbocharger 300 or to passthrough the exhaust turbine 350 of the turbocharger 300 to operate theair compressor 310. The pipe outlet 206 located at the end of theexhaust pipe 202 fluidly communicates with the bypass conduit 620.Specifically, the bypass conduit 620 defines an exhaust inlet 622 whichis fluidly connected to the pipe outlet 206. The exhaust inlet 622 andthe pipe outlet 206 are arranged such that exhaust gas passing from thepipe outlet 206 into the exhaust inlet 622 passes through the inlet 622generally normal to the inlet 622. A central axis 629 (FIG. 13 ) of theexhaust inlet 622 illustrates the general direction of exhaust gas flowinto the bypass conduit 620. In the present implementation, the centralaxis 629 coincides with the center of the circular inlet 622, but thatmay not always be the case.

The bypass conduit 620 is further fluidly connected to the housing 302of the turbocharger 300. More specifically, the bypass conduit 620 ismechanically connected to the turbocharger housing 302 in the presentimplementation by a clamp 303. It is contemplated that the bypassconduit 620 could be an independent apparatus from the turbocharger 300.It is also contemplated that the bypass conduit 620 could be fastened orotherwise mechanically connected to the turbocharger housing 302. It isfurther contemplated that the bypass conduit 620 and the turbochargerhousing 302 could be integrally formed.

The bypass conduit 620 is generally Y-shaped, with an inlet conduitportion 690 extending from the exhaust inlet 622 and branching into twooutlet conduit portions 692, 694 (FIG. 14 ). As such and as is mentionedabove, the bypass conduit 620 serves to selectively direct the exhaustgas which enters through the exhaust inlet 622 either into the exhaustturbine 350 or bypassing the exhaust turbine 350. The turbine outletportion 692 of the bypass conduit 620 (one branch of the Y-shape)fluidly communicates with the turbine inlet 355. A bypass outlet portion694 (the other branch of the Y-shape) allows exhaust gas to bypass theturbocharger 300 to exit the bypass conduit 620 through a bypass outlet626. The bypass outlet portion 694 defines a passage 625 which allowsfor fluid communication between the exhaust inlet 622 and the outlet626. The outlet 626 and the passage 625 can be seen in FIG. 17 . Bestseen in FIG. 16 , the bypass conduit 620 further includes a flow divider628 disposed between the conduit portions 692, 694. The flow divider 628aids in smoothly dividing the exhaust gas flow through the bypassconduit 620, in order to aid in avoiding flow separation or the creationof vortices in the exhaust gas flow. To that end, the flow divider 628is generally shaped and arranged to avoid abrupt edges.

Flow of the exhaust gas through the passage 625 is selectivelycontrolled by a valve 630 disposed in the bypass conduit 620, inconjunction with a system controller 500 controlling the valve 630. Morespecifically, the valve 630 is a valve for selectively diverting exhaustgas away from the turbocharger 300. In the present implementation, thevalve 630 is disposed in the passage 625, and more specifically at avalve seat 623 thereof. It is contemplated that the valve 630 could bedisposed elsewhere in the bypass conduit 620, for example nearer theexhaust inlet 622 and just upstream from the passage 625, depending onthe specific implementation of the valve 630. It is also contemplatedthat in some implementations, the valve 630 could selectively open orclose the turbine outlet portion 692 rather than the bypass passage 625.

With reference to FIGS. 26 to 29 , the valve 630 has a base portion 400and a body portion 402 extending from the base portion 400. The baseportion 400 is configured for pivotably mounting the valve 630 withinthe bypass conduit 620 and thus defines a valve pivot axis 404 aboutwhich the valve 630 is pivotable during use. More specifically, the baseportion 400 is generally cylindrical and has an axle 440 including twoaxle portions 441 extending in opposite directions from a centralsection of the base portion 400. While the axle 440 is made integrallywith the valve 630 in this embodiment, it is contemplated that, in otherembodiments, the axle 440 could be a separate component (e.g., twoseparate axle portions connectable to the base portion 400).

The body portion 402 is the portion of the valve 630 which is used toblock the passage 625. The body portion 402 has an upstream side 406 anda downstream side 408 opposite the upstream side 406. The upstream side406 is exposed, during use, to fluid flow in the bypass conduit 620. Inother words, the upstream side 406 generally faces the inlet 622 whilethe downstream side 408 faces the bypass outlet 626. The body portion402 of the valve 630 is shaped to facilitate control of exhaust gas flowthrough the passage 625. Notably, the body portion 402 has a generallypointed shape defining a rounded tip 410 at a location of the bodyportion 402 furthest from the base portion 400 in a length direction ofthe valve 630 (generally perpendicular to the valve pivot axis 404). Assuch, the body portion 402 of the valve 630 (i.e., the portion of thevalve 630 used to block the passage 625) can be said to be generallyelongated.

A periphery 412 of the body portion 402 generally defines the shapethereof. The periphery 412 includes two opposite lengthwise edges 414that extend from the base portion 400 in a direction generally parallelto the length direction of the valve 630. The periphery 412 alsoincludes a rounded edge 416 defined by the rounded tip 410, and twoconverging angular edges 418 extending between the two lengthwise edges414 and respective ends of the rounded edge 416 (i.e., the angular edges418 connect the lengthwise edges 414 to the rounded edge 416). Theangular edges 418 converge toward each other as the two angular edges418 extend from the two lengthwise edges 414 to the ends of the roundededge 416. Each of the angular edges 418 is thus disposed at an angle θrelative to the length direction of the valve 630. The angle θ may bebetween 10° and 45° inclusively. For instance, in this implementation,the angle θ is approximately 30°.

As shown in FIG. 26 , the body portion 402 of the valve 630 is generallysymmetrical about a plane of symmetry PS bisecting the rounded tip 410.The plane of symmetry PS is perpendicular to the valve pivot axis 404.One of each of the lengthwise edges 414 and angular edges 418 isdisposed on either side of the plane of symmetry PS. Moreover, in thisimplementation, the base portion 402 of the valve 630 is alsosymmetrical about the plane of symmetry PS. However, it is contemplatedthat the valve 630 could not be symmetrical about the plane PS.

A width of the body portion 402, measured in a direction parallel to thevalve pivot axis 404, varies along the length direction of the valve630. For instance, the width of the body portion 402 is largest adjacentthe base portion 400. More specifically, a maximal width W_(max) of thebody portion 402 is measured between the two opposite lengthwise edges414. The width of the body portion 402 decreases at the angular edges418 along the length direction of the valve 630 toward the rounded tip410. Notably, the width of the body portion 402 is smallest at therounded tip 410.

As shown in FIG. 27 , a length L_(V) of the valve 630 is measured fromthe base portion 400 to the rounded tip 410 in the length direction ofthe valve 630. In this implementation, the length L_(V) of the valve 630is greater than or equal to the maximal width W_(max) of the bodyportion 402. Notably, the length L_(V) is greater than the maximal widthW_(max) such that a ratio L_(V)/W_(max) of the length L_(V) of the valve630 over the maximal width W_(max) of the body portion 402 is greaterthan 1. For instance, the ratio L_(V)/W_(max) may be between 1 and 2inclusively. Notably, the ratio L_(V)/W_(max) is between 1.2 and 1.6. Inone particular embodiment, the ratio L_(V)/W_(max) is approximately 1.3.

Furthermore, a ratio W_(max)/R_(T) of the maximal width W_(max) of thebody portion 402 over a tip radius R_(T) of the rounded tip 410 isgreater than 2. For instance, the ratio W_(max)/R_(T) may be between 2and 6 exclusively. In this implementation, the ratio W_(max)/R_(T) isapproximately 3.

As shown in FIG. 26 , the body portion 402 of the valve 630 has a ridge420 disposed on the upstream side 406. Notably, the ridge 420 protrudesfrom a generally planar surface 422 of the upstream side 406. In thisimplementation, a height of the ridge 420 measured from the surface 422is constant. The ridge 420 forms a closed shape which, in thisimplementation, is generally pentagonal. As will be described in moredetail below, the periphery 412 contours part of the ridge 420.

In this implementation, the ridge 420 has five edges including a baseedge 424, two outwardly-extending edges 426 and two inwardly-extendingedges 428. The base edge 424 extends generally parallel to the valvepivot axis 404 and is disposed near the base portion 400 of the valve630. Each outwardly-extending edge 426 extends from a corresponding endof the base edge 424 outwardly toward a corresponding one of thelengthwise edges 414 of the periphery 412 of the body portion 402. Theinwardly-extending edges 428 are generally parallel to correspondingones of the angular edges 418 of the periphery 412 of the body portion402. Each inwardly-extending edge 428 extends from an end of acorresponding one of the outwardly-extending edges 426.

The edges 424, 426, 428 of the ridge 420 meet at corresponding roundedvertices 430 ₁-430 ₅. Notably, the inwardly-extending edges 428 convergeat a distal rounded vertex 430 ₅ which, amongst the vertices 430 ₁-430₅, is furthest from the base portion 400. The distal rounded vertex 430₅ is generally concentric with the rounded edge 416 of the periphery 412of the body portion 402. Notably, the rounded edge 416 of the periphery412 contours the rounded vertex 430 ₅ of the ridge 420. Furthermore, theangular edges 418 and the lengthwise edges 414 contour the inwardly andoutwardly-extending edges 428, 426 respectively.

As shown in FIG. 29 , a cross-sectional profile of the ridge 420, whichcan be observed for example along a plane normal to the length directionof the valve 630, is generally trapezoidal.

With reference to FIGS. 27 to 29 , the body portion 402 of the valve 630also has a peripheral lip 432 protruding on the downstream side 408 ofthe body portion 402. The peripheral lip 432 extends from the periphery412 of the body portion 402. The peripheral lip 432 therefore hasgenerally the same shape as that defined by the periphery 412. Theperipheral lip 432 has a variable height measured from a surface 434 ofthe downstream side 408 of the body portion 402. The height of theperipheral lip 432 adjacent the base portion 400 is greater than theheight of the ridge 420.

The valve 630 as described above is generally shaped to avoid abruptedges to aid in preventing flow separation or the creation of vorticesin the exhaust gas flow within the bypass conduit 620.

In this implementation, the valve 630 is a single-piece component inthat the base portion 400 and the body portion 402 are made integrally.However, it is contemplated that, in alternative implementations, thebase portion 400 and the body portion 402 may be made as separatecomponents and connected to one another to form the valve 630.

With reference to FIG. 12 , an actuator 635 is operatively connected tothe valve 630 to cause the valve 630 to pivot about the valve pivot axis404 (shown in FIG. 26 ). In this implementation, the actuator 635 is aservomotor. It is contemplated that any other suitable type of actuatormay be used in other implementations. The actuator 635 is connected tothe valve 630 via a linkage assembly 636. More specifically, in thisimplementation, the linkage assembly 636 includes three arms 637, 638,639. The arm 637 is connected to the actuator 635 and is rotatablethereby. The arm 638 is connected to the axle 440 of the base portion400 of the valve 630. The arm 639 is connected between the arms 637,638. Rotation of the arm 637 therefore actuates the two other arms 638,639 and causes the valve 630 to pivot between an open position, a closedposition, and intermediate positions as will be described below. It iscontemplated that, in some implementations, the valve 630 could rotate,translate, or be moved otherwise to control exhaust gas flow through thepassage 625.

The valve 630 is controlled to regulate the flow of exhaust gas throughthe turbocharger 300 by selectively blocking or opening a valve opening627 defined by the valve seat 623 of the passage 625. The valve opening627 defined by the valve seat 623 is thus shaped such that itcorresponds to the shape of the body portion 402 of the valve 630 (i.e.,generally elongated and having a rounded tip). The valve 630 ispivotably mounted at the valve seat 623 via the base portion 400 of thevalve 630 and is selectively movable between: an open position in whichexhaust gas flow through the valve opening 627 (and thus the passage625) is substantially unimpeded by the valve 630; a closed position inwhich the valve 630 fully closes the valve opening 627 such that exhaustgas flow through the valve opening 627 is cut-off by the valve 630; andany number of intermediate positions between the open and closedpositions. In this implementation, as shown in FIG. 15 , in its openposition, the valve 630 is at approximately 45° (measured from the valveseat 623—i.e., 0° corresponding to the closed position of the valve630). Moreover, in the open position, the valve 630 contacts a wall ofthe bypass conduit 620 on a side opposite the flow divider 628, but thismay not be the case in all implementations.

A cross-section of the bypass conduit 620 is illustrated in FIGS. 14 to16 to show the different positions of the valve 630. FIG. 14 illustratesthe closed position; FIG. 15 illustrates the open position (alsoillustrated in FIG. 25 ); and FIG. 16 illustrates one of the manypossible intermediate positions of the valve 630. As can be seen, thevalve 630 is oriented in the bypass conduit 620 such that the roundedtip 410 is downstream of the base portion 400. That is, in the open,closed and intermediate positions, the rounded tip 410 of the valve 630is downstream of the base portion 400. The exhaust gas flow through thebypass conduit 620 for each of the relative positions of the valve 630will be described in more detail below. As can be seen in FIG. 14 , inits closed position, the valve 630 contacts the valve seat 623. Morespecifically, in the closed position, the ridge 420 of the body portion402 of the valve 630 sits against the valve seat 423.

In relation to a circular valve, the generally elongated shape of thevalve 630 as described above establishes a more linear relationshipbetween the mass flow of exhaust gas through the opening 627 and theangle at which the valve 630 is open. In other words, a greater controlof the mass flow of exhaust gas through the opening 627 is made possibleby the shape of the valve 630. Consequently, backpressure within theexhaust system 600 caused by opening the valve 630 can be controlledmore precisely than with a circular valve. This can be seen in the chartof FIG. 30 which illustrates a percentage mass flow through an openingas a function of a position of a valve (expressed as a percentage—0%corresponding to the closed position of the valve; 100% corresponding tothe fully open position of the valve) for the valve 630 of the presenttechnology and for a circular valve. The percentage mass flow reaches100% when the valve is in the open position (for the valve 630 thiscorresponds to a 45° angle, but is approximately 90° for the circularvalve). Notably, the performance curve P1 represents the percentage massflow through the opening 627 as a function of the position of the valve630 in accordance with the present technology. By way of contrast, theperformance curve PA represents the percentage mass flow through acircular opening as a function of the position of its correspondingcircular valve. As can be seen, in accordance with the presenttechnology, the relationship between the mass flow percentage throughthe opening 627 and the position of the valve 630 is markedly morelinear than for the circular valve, particularly at smaller angles ofthe valve (e.g., below 45%—i.e., below 20° for the valve 630).

The exhaust system 600 further includes the system controller 500, whichis operatively connected to an engine control unit (or ECU) and/or theelectrical system (not shown) of the snowmobile 10. The engine controlunit is in turn operatively connected to the engine 26. As will bedescribed in more detail below, the system controller 500 is alsooperatively and communicatively connected to an atmospheric pressuresensor 504, also referred to as an air intake sensor 504, for sensingthe atmospheric or ambient air pressure of the intake air coming intothe air intake system 100. It should be noted that the atmosphericpressure sensor 504, also referred to herein as an intake pressuressensor 504, senses the air pressure in the primary airbox 120, and assuch measures the air intake pressure from air entering either from theambient air around the snowmobile 10 and/or the air entering the primaryairbox 120 from the turbocharger 300.

The actuator 635 for selectively moving the valve 630 is communicativelyconnected to the system controller 500 such that the position of thevalve 630 is controllable thereby. It is contemplated that the valve 630could be differently controlled or moved, depending on theimplementation.

As is illustrated in the schematic diagram of FIG. 8 and as will bedescribed in more detail below, the system controller 500 is alsooperatively connected to the throttle valve position sensor 588 fordetermining the position of the throttle valve 39, a rate of opening ofthe throttle valve 39, or both. In some modes of operation of theexhaust system 600, the valve 630 is selectively moved based on thethrottle valve position determined by the throttle valve position sensor588. In some modes of operation of the exhaust system 600, the valve 630is selectively moved based on the rate of change of the throttle valveposition or the rate of opening of the throttle valve 39, as determinedby the throttle valve position sensor 588.

As is illustrated schematically in FIG. 8 and as will also be describedin more detail below, the system controller 500 is further connected toan exhaust pressure sensor 590 for sensing the backpressure of theengine 26. Backpressure, also known as the exhaust gas pressure, isunderstood to be the resistance to the flow of the exhaust gas betweenthe engine 26 and an outlet of the muffler 650 due, at least in part, totwists, bends, obstacles, turns and sharp edges present in the variouscomponents of the exhaust system 600. In the present technology,reducing backpressure can assist in optimizing performance of the engine26, as high backpressure can negatively impact the efficiency of theengine performance. Reducing the amount of backpressure in the exhaustsystem 600 may also have the effect of reducing what is known as “turbolag”, which is a delay in the response of a turbocharged engine afterthe throttle lever 86 has been moved for operating the throttle system.

In the present implementation, the exhaust pressure sensor 590 isdisposed near the exhaust outlet 206 of the exhaust pipe 202. It iscontemplated that the exhaust pressure sensor 590 could be differentlyarranged, depending on details of a particular implementation. In someimplementations, the system 600 could further include a differentialsensor for determining a pressure differential between the air intakepressure entering the engine 26 and the exhaust pressure of exhaust gasexiting the engine 26. It is also contemplated that the differentialsensor could replace one or both of the intake pressure sensor 504 andthe exhaust pressure sensor 590 in some implementations.

As is also illustrated in FIG. 8 , the system controller 500 is furtherconnected to several sensors for monitoring various exhaust systemcomponents. The system controller 500 is communicatively connected to anexhaust pipe temperature sensor 512 to detect the temperature of theexhaust pipe 202. Similarly, the system controller 500 iscommunicatively connected to a muffler temperature sensor 550 to detectthe temperature of the muffler 650. These sensors 512, 550 could be usedto monitor possible overheating or temperature imbalances, as well as toprovide information to the system controller 500 to use in controlmethods such as those described herein. In order to determine an enginespeed of the engine 26, the system controller 500 is furthercommunicatively connected to an engine sensor 586 disposed incommunication with the engine 26.

The exhaust system 600 further includes an exhaust collector 640 fluidlyconnected to the bypass conduit 620 and the turbocharger 300. Theexhaust collector 640, shown in isolation in FIGS. 20A to 20C, includesan inlet 642 through which the exhaust collector 640 receives exhaustgas from both the bypass conduit 620 and the exhaust turbine 350.

More specifically, the inlet 642 receives exhaust gas that bypasses theexhaust turbine 350 and exits through the outlet 626 of the bypassconduit 620. The inlet 642 also receives exhaust gas that has passedthrough the exhaust turbine 350 from an outlet 315 of the turbochargerhousing 302. The inlet 642 includes two portions: a lower portion 643and an upper portion 645. The lower and upper portions 643, 645 areintegrally connected to define a peanut-shaped opening in the inlet 642.It is contemplated that the inlet 642 could be differently shapeddepending on the implementation.

The lower portion 643 is fluidly connected to the housing 302 to receiveexhaust gas therethrough from the exhaust turbine 350 through the outlet315. The upper portion 645 is fluidly connected to the bypass conduitoutlet 626 to receive therethrough the exhaust gas that has bypassed theexhaust turbine 350. The exhaust collector 640 also includes an outlet646, through which exhaust gas passing into the exhaust collector 640exits. It is contemplated that the two inlet portions 643, 645 could beseparated in some implementations, such that the exhaust collector 640could be generally Y-shaped for example.

The exhaust collector 640 is bolted to the housing 302 and the bypassconduit 620 using through-holes 641 defined in a periphery of the inlet642. It is contemplated that the exhaust collector 640 could bedifferently connected to the turbocharger housing 302 and the bypassconduit 640 in different implementations. It is also contemplated thatthe exhaust collector 640 could be integrally formed with the bypassconduit 620 and/or the turbocharger housing 302.

With reference to FIG. 10 , the exhaust system 600 includes a muffler650. The muffler 650 includes one muffler inlet 654 through which toreceive exhaust gas from the exhaust system 600. The muffler 650 isfluidly connected to the collector outlet 646 of the exhaust collector640. The muffler inlet 654 and the collector outlet 646 are held inplace by springs as can be seen in the Figures. It is contemplated thatdifferent methods could be employed to connect the muffler 650 to theexhaust collector 640. As can be seen in the Figures, the muffler 650includes only the single inlet 654 for receiving exhaust gas bothbypassing and passing through the exhaust turbine 350.

Flow of the exhaust gas through the exhaust system 600, specificallybetween the exhaust pipe 202 and the muffler 650, will now be describedin more detail. As is described briefly above, the valve 630 in thebypass conduit 620 selectively controls the flow of exhaust gas eitherinto the exhaust turbine 350 or bypassing the exhaust turbine 350 bysending the exhaust gas out through the conduit outlet portions 692,694.

In the present technology, the bypass conduit 620 is designed andarranged to balance two competing interests: the first being to allowfor efficient exhaust gas flow when bypassing the turbocharger 300 inorder to operate the engine 26 as a naturally aspirated engine 26, andthe second being not impeding efficient operation of the turbocharger300 when desired. In traditional turbo-charged engines, all exhaust gaswould be directed to the turbocharger 300, with an associated bypassonly being used in the case of too much exhaust gas flow into theturbocharger. In the present technology, exhaust gas can be directedeither to bypass the turbocharger 300 for naturally aspirated operationor into the turbocharger 300 for turbo-charged operation. The inclusionof the intake bypass valve 123 further aids in allowing for naturallyaspirated operation or turbo-charged operation of the engine 26. As isdescribed above, the intake bypass valve 123 allows for atmospheric orambient airflow into the primary airbox 120 when the pressure in theprimary airbox 120 falls below a threshold, due the turbocharger 300 notoperating or spooling up and thus not providing sufficient compressedair to the primary airbox 120. By including both the valve 630 and thebypass valve 123, each of which are independently operated, both airintake and exhaust gas are managed to allow for naturally aspirated orturbo-charged operation of the engine 26.

As is mentioned above, exhaust gas entering the bypass conduit 620 flowsgenerally parallel to the central axis 629 of the inlet 622. As can beseen in FIGS. 13 to 16 , the central axis 629, and thus the center ofthe flow of exhaust gas, is directed to the turbine outlet portion 692side of the flow divider 628. As the flow divider 628 is situated towardthe bypass side with respect to the central axis 629, it should beunderstood that more than half of the exhaust gas flow is thereforeinitially directed toward the turbine outlet portion 692.

On the bypass outlet portion 694 side of the central axis 629 (to theleft of the axis 629 in the Figures), it can also be seen that some ofthe exhaust gas flow, parallel to the central axis 629, is directedtoward the opening 627. As the conduit inlet 622 and opening 627 of thepassage 625 are at least partially aligned along the direction of thecentral axis 629, at least a portion of the exhaust gas entering theconduit inlet 622 parallel to the flow axis flows unobstructed into thebypass passage 625 when the valve 630 is in the open position. As theengine 26 is intended to be naturally aspirated in standard operation,at least a portion of exhaust gas flowing generally directly through thebypass conduit 620 and into the exhaust collector 640, with a minimum ofturns, bends, etc. further assists in decreasing backpressure, again inthe aims of optimizing engine performance.

It should be noted that, as will be described further below, thepercentage of exhaust gas flow directed toward each of the outputconduits 692, 694 does not necessarily correspond to the percentage ofexhaust gas that flows therethrough.

The two different flow patterns of exhaust gas entering the bypassconduit 620 will now be described in reference to flow paths 670, 675schematically illustrated in FIG. 8 . Depending on the position of thevalve 630, the exhaust gas can flow along a bypass exhaust flow path670, a turbine exhaust flow path 675, or a combination of the two paths670, 675.

Exhaust gas flowing along the bypass exhaust flow path 670 passesthrough the passage 625, which is not blocked by the valve 630 when thevalve 630 is in the open position. The bypass exhaust flow path 670 isdefined from the exhaust inlet 622 of the bypass conduit 620 to theexhaust collector 640. Exhaust gas flowing along the bypass exhaust flowpath 670 passes through the exhaust inlet 622, then through the bypassconduit 620, and then into the exhaust collector 640. Specifically,exhaust gas flowing along the bypass exhaust flow path 670 is receivedin the upper portion 645 of the inlet 642.

The turbine exhaust flow path 675 is similarly defined from the exhaustinlet 622 of the bypass conduit 620 to the exhaust collector 640.Exhaust gas flowing along the second exhaust flow path passes throughthe exhaust inlet 622, then through the turbine outlet portion 692 ofthe bypass conduit 620, then through the exhaust turbine 350, and theninto the exhaust collector 640. Specifically, exhaust gas flowing alongthe turbine exhaust flow path 675 is received in the lower portion 643of the inlet 642.

For each flow path 670, 675, exhaust gas passes out of the collectoroutlet 646 and into the muffler inlet 654. The single muffler inlet 654of the muffler 650 receives the exhaust gas from both the bypass exhaustflow path 670 and turbine exhaust flow path 675.

Even though the majority of exhaust gas flow is oriented toward theturbine outlet portion 692, a majority of the exhaust gas entering theexhaust inlet 622 flows along the bypass exhaust flow path 670, throughthe bypass outlet portion 694, when the valve 630 is in the openposition. The flow path 675 through the exhaust turbine 350, designed toturn under pressure from exhaust gas flowing therethrough, is morerestrictive and causes more backpressure than the flow path 670 throughthe bypass passage 625. More of the exhaust gas is therefore directedthrough the passage 625, even if the initial flow direction is towardthe turbine outlet portion 692. It should be noted that a portion of theexhaust gas entering the bypass conduit 620 will still flow through theexhaust turbine 350 even when the valve 630 is fully open.

When the valve 630 is in the closed position, a majority (generally all)of the exhaust gas entering the exhaust inlet 622 flows along theturbine exhaust flow path 675. As is illustrated schematically, exhaustgas flowing along the turbine exhaust flow path 675 is deflected by thevalve 630, as the valve 630 blocks the passage 625 in the closedposition. As some of the exhaust gas entering through the conduit inlet622 flows in parallel to the central axis 629, at least a portion of thevalve 630 is contacted by, and diverts, exhaust gas entering the inlet622.

As is mentioned above, the valve 630 can also be arranged in anintermediate position, such as that illustrated in FIG. 16 (just as onenon-limiting example). With the valve 630 in the intermediate position,a portion of the exhaust gas is allowed through the passage 625 tobypass the exhaust turbine 350 and a portion of the exhaust gas isdeflected through the turbine outlet portion 692 toward the exhaustturbine 350. In the intermediate position, at least a portion of thevalve 630 is contacted by the exhaust gas entering through the conduitinlet 622 and flowing parallel to the axis 629.

The exhaust gas thus flows along both of the bypass exhaust flow path670 and the turbine exhaust flow path 675 when the valve 630 is in oneof the intermediate positions. The ratio of the portion of exhaust gasflowing along the bypass exhaust flow path 670 to the portion of exhaustgas flowing along the turbine exhaust flow path 675 depends on variousfactors, including at least the angle at which the valve 630 isarranged. Generally, the closer the valve 630 is to the open position,the more exhaust gas will flow along the bypass exhaust flow path 670and vice versa.

As will be described in more detail below, the valve 630 is used tomanage exhaust gas flow through the flow paths 670, 675. For example, insome scenarios, the valve 630 is selectively moved to the closedposition (or toward the closed position) when the engine 26 is operatedbelow a threshold atmospheric pressure. In such a scenario, theturbocharger 300 could be used to help boost engine performance when thesnowmobile 10 climbs in altitude, where the air is thinner and as suchless oxygen will enter the engine 26 (having a detrimental effect onperformance).

Regardless of the position of the valve 630, in this implementation,there is no physical barrier blocking air flow between the exhaust inlet622 and the turbine inlet 355. As is mentioned above, a portion of theexhaust gas entering through the bypass inlet 622 passes through theturbine outlet portion 692 and enters the exhaust turbine 350 throughthe turbine inlet 355, even when the valve 630 is in the open position.The relatively small portion of exhaust gas entering the exhaust turbine350 aids in creating a pressure difference between positions upstreamfrom the exhaust turbine 350 and downstream therefrom. This pressuredifference generally improves the responsiveness of the turbocharger300, generally making the exhaust turbine 350 spool up more rapidly andassisting in decreasing the turbo lag.

Similarly, there is no physical barrier closing the turbine outlet 315when the exhaust gas flows along the bypass exhaust flow path 670. Assuch, flow of exhaust gas out of the bypass outlet 626 causes an airpressure reduction in the turbine outlet 315. This low pressure zonealso assists in decreasing the turbo lag and in increasing the spool upspeed. It is also noted that there is also no barrier closing the bypassoutlet 626 when the exhaust gas is directed to the turbine exhaust flowpath 675 and flowing out of the turbine outlet 315.

The exhaust system 600, according to the present technology and asdescribed above, is generally intended to be operated as a naturallyaspirated engine system, with the exhaust gas generally bypassing theexhaust turbine 350, other than in specific scenarios where additionalboost from the turbocharger 300 is necessitated. This is in contrast tosome standard turbo-charged engine arrangements, where a turbocharger isused in standard operation and a turbocharger bypass is used to preventoverload of the compressor.

In the arrangement and alignment of the exhaust system 600 of thepresent technology, in contrast to conventional turbochargerarrangements, a majority of the exhaust gas flows through the passage625 when the valve 630 is in the open position (described above).Exhaust gas flow, especially to allow the gas to bypass the turbocharger300 without creating excessive backpressure, is further managed by thecomparative cross-sections of the two flow paths 670, 675. Specifically,in the present technology, the area of the opening 627 of the passage625 (for the bypassing flow path 670) and the intake area 354 of theexhaust turbine 350 (in the turbine flow path 675) are of similardimensions.

The arrangement of the relative areas of the openings 627, 355 in thetwo flow paths 670, 675 allows exhaust gas to both bypass the exhaustturbine 350 without creating excessive backpressure (which can bedetrimental to operation of the engine 26) while still allowing goodexhaust gas flow through the turbine inlet 355 when the turbine 300 issolicited. According to the present technology, the area of the opening627 is generally between 0.75 and 1.25 times the area 354 of theturbocharger inlet 355. In the present implementation, the area 354 ofthe turbocharger inlet 355 is slightly greater than the area of theopening 627. It is contemplated, however, that the area of the opening627 could be greater than the area 354 of the turbocharger inlet 355 insome implementations.

In further contrast to conventional turbocharger arrangements, thebypass outlet 626 has been specifically arranged such that there is notan excessive amount of deviation of the exhaust flow necessary for theflow to travel from the bypass conduit inlet 622 to the bypass outlet626. A normal of the bypass outlet 626 is at an angle of about 20degrees to the central axis 629 in the present implementation (althoughthe exact angle could vary). With this arrangement, a portion of theexhaust gas entering the inlet 622, illustrated between lines 601 and603 in FIG. 15 , both parallel to the central axis 620, will passdirectly through the bypass conduit 620, meaning through the passage 625and the opening 627, and out of the bypass outlet 626 without deviating.This is true even for a plurality of positions of the valve 630 betweenthe fully open and fully closed positions.

When the snowmobile 10 is not being operated below a thresholdatmospheric pressure, the exhaust system 600 will tend to send exhaustgas along the bypass exhaust flow path 670 bypassing the exhaust turbine350 and the engine 26 will operate as a naturally aspirated engine 26.When the snowmobile 10 is operated below such a threshold air intakepressure, for example at high altitudes/low atmospheric pressure, thevalve 630 will move toward the closed position (either partially orcompletely) to send some or all of the exhaust gas to the exhaustturbine 350 to provide boost to the engine 26. More details pertainingto operation of the valve 630 with respect to operating conditions willbe provided below.

Example Operation of the Exhaust System

With reference to FIGS. 31 and 32 , one non-limiting illustrativescenario of operation of the exhaust system 600 will now be described.Different implementations of specific methods will be described in moredetail with reference to FIGS. 21 to 23 . It should be noted that thisis simply one non-limiting example to provide a high-level understandingof the general operation of the exhaust system 600, and differentimplementations and details will be set out below.

Broadly stated, the system controller 500 retrieves predeterminedpositions of the valve 630 from data tables (datasets) based on throttleposition (TPS) and engine speed (RPM). Depending on the particular modeof operation (described further below), the exhaust pressure, inputpressure, or a difference between the two are simultaneously monitoredby comparing their values to similar predetermined pressure datasets. Aflow-chart 950 generally depicting the steps taken by the systemcontroller 500 when controlling the valve 630 in the presentillustrative scenario is illustrated in FIG. 31 .

First, the controller 500 determines whether the snowmobile 10 is beingoperated near sea-level or nearer to a high altitude. The relativealtitude (high or low) is generally determined by the intake pressuresensor 504 by measuring the ambient air pressure entering the air intakesystem, but in some cases the snowmobile 10 could include an altimetercommunicatively connected to the system controller 500 for determiningthe altitude. The system controller 500 can then retrieve thepredetermined datasets of valve position and pressure corresponding tooperation of the snowmobile 10 at the relevant altitude range. In orderto avoid inaccurate altitude readings by the intake pressure sensor 504caused by additional pressure created by the turbocharger 300, thealtitude-related pressure reading is taken when the RPM and the TPSoutputs are below a predetermined level that corresponds to an operatingstate of the snowmobile 10 where no boost pressure from the turbocharger300 should be created. It is also noted that datasets corresponding todifferent altitudes, other than low or high, could be used. Datasetscorresponding to more than two altitudes are also contemplated.

Following determination that the snowmobile 10 is either at high or lowaltitude, the system controller 500 then determines if the valve 630should be adjusted according to a “coarse” adjustment regime or a “fine”adjustment regime. This determination is performed by comparing anactual boost pressure (the current air intake pressure which issupplemented by the turbocharger 300) with a predetermined desired boosttarget pressure based on a dataset of TPS vs RPM. The actual boostpressure produced by the turbocharger 300 is determined by the intakepressure sensor 504. A desired boost target pressure for the current TPSand RPM values is determined from a predetermined dataset, an examplepredetermined desired boost target pressure dataset 975 being shown inFIG. 32 . When the actual boost from the turbocharger 300 is within apredetermined range or threshold of the desired boost target (forexample within 5, 10, 15 mbars of the desired boost), the fine regimewill be used. Otherwise, the coarse regime will be used. Depending onthe specific implementation, the predetermined range could be modifieddepending on factors such as ambient air temperature, altitude etc. Itis further noted that the predetermined range for switching from thecoarse regime to the fine regime could, in some cases, be different thanthe predetermined range for switching from the fine regime to the coarseregime. This hysteresis is introduced into the coarse/fine determinationapproach to aid in limiting rapid switching between the two controlregimes. If the threshold differences for switching between the coarseand fine adjustment regimes were the same, for example, each time thepressure difference is slightly below or above the threshold the methodcould switch regimes in a rapid alternation between the coarse and fineadjustment regimes. This could be unnecessarily inefficient especiallywhen the pressure difference is oscillating around the threshold value.

When operating in the coarse adjustment regime, also known as a dynamicregime, the backpressure is simultaneously monitored and controlledaccording to a pressure dataset, in order to ensure that movement of thevalve 630 to increase boost pressure does not cause a detrimentalincrease in backpressure. A sample pair of a valve position dataset 960and a pressure dataset 970 are illustrated in FIG. 33 (the values aresimply illustrative and are not meant to be limiting). In the case wherepressure dataset 970 is being used in the coarse regime, the outputvalues will represent a maximum value difference between the exhaustpressure and the intake pressure as will be described in more detailbelow.

During control of the valve 630, if the backpressure rises above acertain amount for the current operating conditions (e.g. RPM and TPS),the performance of the engine 26 could be negatively affected or atleast not optimal. To impede this from happening, the representation ofthe maximum backpressure as determined in the dataset 970 from thecurrent TPS and RPM values, is compared to the actual backpressure, asdetermined from the exhaust pressure minus the intake pressure obtainedfrom the exhaust pressure sensor 590 and the intake pressure sensor 504respectively. If the actual backpressure exceeds the value from thedataset 970, the system controller 500 will apply a correction to thevalve position dataset 960 in order to move the valve 630 to a positionthat maintains the backpressure within an acceptable range, i.e. theactual pressure difference below that obtained from the dataset 970. Insome cases a correction factor could be mathematically applied acrossthe dataset 960; in some implementations a different predetermineddataset 960 could be retrieved.

In the fine adjustment regime, fine adjustment tables, also referred toas static datasets, are used when there is a small difference betweenthe actual boost pressure and the desired boost pressure as mentionedabove. In contrast to the approach taken in coarse adjustment, the fineadjustments are made to approach and maintain the optimal intakepressure (boost pressure) into the engine 26. As small adjustments tothe position of the valve 630 should not have a drastic effect on thebackpressure, during the fine adjustment regime the backpressure may notbe continuously monitored, as it is in the coarse regime. As with thecoarse regime, the fine regime uses a valve position dataset similar tothat of dataset 960, which is based on the actual TPS and RPM values,and a pressure dataset similar to that of 970 also based on the actualTPS and RPM values. The pressure dataset 970, when in the fine regime,includes values that represent only the intake pressure and that are tobe compared to the actual intake pressure measure by the intake pressuresensor 504. The difference between the output from the dataset 970, whenin the fine regime, and that of the actual intake pressure, willdetermine a correction factor to be applied to the valve position fromdataset 970.

During operation, the system controller 500 continuously reevaluates thealtitude and coarse/fine determinations, as there will be changes to thethrottle and RPM positions as the snowmobile 10 is operated, which willalso change the exhaust and intake pressures as the valve 630 iscontrolled to improve operation of the engine 26, and/or changes in thealtitude at which the snowmobile 10 is being operated as it travels overterrain.

With reference to FIGS. 21 to 23 , different methods of controlling theflow of exhaust gas from the engine 26 will be described. Each will bedescribed in more detail below. Briefly, the methods 700, 750, 800 aimto balance providing optimized boost to the engine 26 based on operatingconditions (in the form of compressed air provided by the turbocharger300) with the detrimental increase of backpressure that can be causedwhile the turbocharger 300 is spooling up. This control is provided bythe valve 630. As is briefly mentioned above, operation of the exhaustsystem 600 with the valve 630 assists in preventing backpressure fromimpeding engine functionality, as the exhaust gas flows out through thebypass conduit 620. By closing the valve 630, exhaust gas is directedinto the exhaust turbine 350 such that the turbocharger 300 providesadditional air to the engine 26, but this exhaust flow path 675 alsoincreases the backpressure. In some implementations of the methods,adjustments can be made to the positioning of the valve 630 to balancethe need for additional compressed air versus negatively impactingengine operation through increased backpressure.

Operation Based on a Pressure Reading

Operation of the exhaust system 600 in accordance with different methodsaccording to the present technology will now be described in moredetail. In reference to FIG. 21 , a non-limiting implementation ofcontrolling operations in the exhaust system 600 is set out in the formof a method 700 for controlling a flow of exhaust gas from the engine26. The method 700 is performed by the system controller 500 accordingto the present technology. In some implementations, it is contemplatedthat an additional or substitute computational system could beimplemented to perform the method 700.

The method 700 begins at step 705, with determining at least onepressure of the engine 26. Based on one or more of the pressuresdetected for the engine 26, the method 700 determines how to positionthe valve 630 in order to optimize or improve performance of the engine26. As will be described in more detail below, the valve 630 could bepositioned based on, but is not limited to, exhaust pressure, air intakeand/or atmospheric pressure, and the desired or actual boost pressure.

The method 700 then continues at step 720 with moving the valve 630 tothe closed position, the open position, or an intermediate positionbased at least on the pressure determined in step 710. Depending on thedetermined pressure, the valve 630 is moved to direct more or lessexhaust gas into the exhaust turbine 350. In some cases, the desiredposition of the valve 630 will correspond to the current position of thevalve 630, and as such the valve 630 would not be moved.

In some implementations, determining a pressure at step 705 includesdetermining a pressure differential between an actual boost pressure ofair flowing into the engine 26 and a predetermined boost pressure of airflowing into the engine 26 at sub-step 710.

In some implementations, the determining the pressure differential atsub-step 710 is performed in two sub-steps. First the actual boostpressure is determined at sub-step 712. The actual boost pressure isdetermined based on readings from the intake pressure sensor 504, todetermine the air intake pressure coming from the turbocharger 300. Itis contemplated, however, that a different sensor and/or operationalvalue could be used to determine the actual boost pressure.

The predetermined boost pressure is determined at sub-step 714. Thepredetermined boost pressure is a boost pressure calculated orpreviously determined to be matched generally to the operatingconditions of the engine 26, such that operation of the engine 26 isbest optimized. The predetermined boost pressure is retrieved from acomputer-accessible storage medium 507 operatively connected to orincluded in the system controller 500 (shown schematically in FIG. 8 ).It is contemplated that additional sensors could be included in theexhaust system 600 and utilized in the method 700.

In some implementations, determining the predetermined boost pressure atsub-step 714 includes at least one of: determining, by the engine sensor586, the engine speed of the engine 26, determining a throttle valveposition of the throttle valve 39 of the engine 26 by the throttle valveposition sensor 588, determining a throttle lever position by theposition sensor of the throttle lever 86, and determining a rate ofthrottle valve opening of the throttle valve 39. In someimplementations, the rate of throttle valve opening could be determinedinstead or in addition to determining the throttle valve position. Thepredetermined boost pressure is then retrieved from the computer-basedstorage medium 507, based on the determined engine speed, throttle valveposition, throttle lever position, and/or rate of throttle valveopening.

It is contemplated that the sub-steps 712, 714 could be performed in anyorder or simultaneously, depending on the specific implementation and/oroperational scenario. In some implementations, it is contemplated thatthe snowmobile 10 could include a differential sensor for determiningthe pressure differential at sub-step 710 in a single measurement.

In some implementations or iterations, the method 700 could furtherinclude determining that the difference between the predetermined boostpressure and the actual boost pressure, as determined in sub-step 710,is less than a difference threshold. The difference threshold generallyindicates whether movement of the valve 630 in order to bring the actualboost pressure more closely in line with the predetermined boostpressure will need to be a coarse adjustment (if the difference is abovethe threshold) or only needs to be a fine adjustment (if the differenceis below the threshold).

Based on the difference being less than the difference threshold, themethod 700 then continues with determining a desired valve position ofthe valve 630 from a fine adjustment data set. The fine adjustment dataset, based on at least one of the throttle position and the engine speedas determined above, relates to fine, or minor, adjustments to theposition of the valve 630 needed in order to provide the desiredpressure in the engine 26 by decreasing the difference between thepredetermined boost pressure and the actual boost pressure. The method700 then continues with moving, following determining the desired valveposition, the valve 630 toward the desired valve position.

Based on the difference being greater than the difference threshold, themethod 700 then similarly continues with determining a desired valveposition of the valve 630 from a coarse adjustment data set. The coarseadjustment data set, based on at least one of the throttle position andthe engine speed as determined above, relates to coarse, or larger,adjustments to the position of the valve 630 needed in order to providethe desired pressure in the engine 26 by decreasing the differencebetween the predetermined boost pressure and the actual boost pressure.The method 700 then continues with moving, following determining thedesired valve position, the valve 630 toward the desired valve position.

In some implementations, the method 700 could be done iteratively, suchthat when the difference between the predetermined boost pressure andthe actual boost pressure is large, coarse adjustments are made toreduce the difference. Once the difference between the predetermined andactual boost pressure are reduced below the threshold, then fineadjustments would be used. Use of coarse and fine adjustments is simplyone non-limiting example of controlling adjustment of the position ofthe valve 630. It is also contemplated that the adjustments could bepartitioned into three or more datasets. For example, two thresholdscould be used to split the adjustments into “large coarse adjustments”,“small coarse adjustments”, and “fine adjustments”. It is alsocontemplated that a single data set could be utilized for determining adesired valve position.

In some implementations or iterations of the method 700, the determiningthe pressure differential at sub-step 710 includes determining adifference between an intake air pressure of air flowing to the engine26, and an exhaust gas pressure of exhaust gas flowing out of the engine26, in place of determining the difference between predetermined andactual boost pressures. In such an implementation, the method 700 wouldthen include determining the intake air pressure by the intake pressuresensor 504 and determining the exhaust gas pressure by the exhaustpressure sensor 590.

The method 700 would then further include determining a predeterminedpressure differential between the exhaust gas pressure and the intakeair pressure. Similar to the predetermined boost pressure, thepredetermined pressure differential corresponds to the optimal orpreferred difference between the exhaust and intake air pressures whichcorrespond to better operation of the engine 26 for the currentoperating conditions. For example, the predetermined pressuredifferential could be set based on engine parameters such as enginespeed such that the engine 26 generally has the air volume necessary forproper functioning, without creating too much backpressure. In someimplementations, the predetermined pressure differential could bedetermined based on, but is not limited to: throttle position and enginespeed.

In such an implementation, the method 700 then continues withdetermining that a difference between the pressure differential and thepredetermined pressure differential is non-zero. The non-zero differenceindicates simply that the actual pressure differential is not at thepredetermined pressure differential and thus the engine 26 may not beoperating optimally. The method 700 thus then continues with moving thevalve 630 based on the difference being non-zero to the open position,the closed position, or one of the intermediate positions. In someimplementations, the position to which the valve 630 is moved coulddepend on whether the actual pressure differential is greater or lessthan the predetermined pressure differential.

In some implementations or iterations of the method 700, the method 700includes determining that the intake air pressure is below a thresholdatmospheric pressure. As with the above steps, determination of theintake air pressure includes measurement of the pressure by the airintake pressure sensor 504. The system controller 500 could thendetermine if the measured air pressure of air entering the engine 26 isbelow some predetermined threshold. For example, the threshold could beset based on engine parameters such that the engine 26 generally has theair volume necessary for proper functioning. It is also contemplatedthat the threshold atmospheric pressure may be a predetermined range ofatmospheric pressure. In one non-limiting example, intake air pressurecould fall below the threshold when the snowmobile 10 is climbing amountain and increasing in altitude.

Then, based at least on the intake air pressure being below thethreshold atmospheric pressure, the method 700 could continue withmoving the valve 630 to or toward the closed position (if the valve 630is in either the open or intermediate position). This would begin, orincrease, operation of the turbocharger 300. As such, when the engine 26is not getting sufficient air for good or sufficient operation, forinstance when the snowmobile 10 is being operated at high altitudes, theturbocharger 300 can be spooled up to provide compressed air to theengine 26 (as is described above).

In some implementations or iterations of the method 700, the method 700could further include determining that the backpressure is too high andopening up the valve 630 to maintain a balance between increasing intakeair pressure to the engine 26 and allowing backpressure to ease throughopening of the valve 630.

Subsequent to moving the valve 630 to or toward the closed position, themethod 700 could further include determining that the exhaust gaspressure is above a threshold exhaust gas pressure. As is mentionedabove, the exhaust gas pressure is measured by the exhaust pressuresensor 590; the system controller 500 then compares the measurement tothe determined backpressure threshold.

Based on the exhaust gas pressure being above the threshold exhaust gaspressure, the method 700 then continues with repositioning the valve 630to either the open position or an intermediate position such thatexhaust gas flows at least partially along the bypassing exhaust gasflow path 670. By opening up the valve 630 such that an increasedportion of the exhaust gas flows out through the bypass portion 620, thebackpressure is eased. Depending on the iteration of the method 700, thevalve 630 could be moved to only a small degree, or in some cases movedall the way to the open position. In some implementations, the change inposition of the valve 630 could be proportional or directly related toan increase of exhaust gas pressure after moving the valve 630 to theclosed position.

In some implementations or iterations of the method 700, the valve 630could be moved back to the open position once the snowmobile 10 isoperated at atmospheric pressures above the threshold used above tobegin use of the turbocharger 300. In one non-limiting example, thevalve 630 could be opened back up, partially or fully to the openposition, when the snowmobile 10 decreases in altitude and theatmosphere surrounding the snowmobile 10 becomes richer.

In such a scenario, the method 700 could further include determining (bythe intake pressure sensor 504 and the system controller 500) that theintake air pressure is above the threshold intake air pressure,subsequent to moving the valve 630 to or toward the closed position.Then, based on the intake air pressure being above the threshold intakeair pressure, the method 700 could continue with moving the valve 630such that a majority or more of the exhaust gas flows along the bypassexhaust flow path 670.

It is contemplated that the method 700 could include additional ordifferent steps, either to perform additional functions and/or toperform the steps described above. It is also contemplated that thesteps described above could be performed in an assortment of differentsequences, depending on for example user preferences, and is not limitedto the order set forth in the explanation above.

Operation Based on Exhaust Gas Pressure

In reference to FIG. 22 , a non-limiting implementation of controllingoperations in the exhaust system 600 is set out in the form of a method750. The method 750 is performed, at least in part, by the systemcontroller 500 according to the present technology. In someimplementations, it is contemplated that an additional or substitutecomputational system could be implemented to perform the method 750.

The method 750 begins at step 760 with determining that an exhaust gaspressure of air flowing out of the engine 26 is above a thresholdexhaust gas pressure, where the valve 630 is in either the closedposition or an intermediate position, where a majority of the exhaustgas is flowing along the turbine exhaust flow path 675. The exhaust gaspressure is determined by the exhaust pressure sensor 590 and the systemcontroller 500 in the present implementation, as is noted above. In someimplementations, the valve 630 could have been moved to the closedposition based on a decrease in atmospheric pressure surrounding thesnowmobile 10, similar to the scenario described above in relation tothe method 700. It is also contemplated that the valve 630 could havebeen moved to or toward the closed position for an alternative reason.For one non-limiting example, the valve 630 could have been moved to theclosed position to provide more air to the engine 26, via the aircompressor 310, based on insufficient performance of the engine 26.

The method 750 then continues, at step 760, with moving the valve 630 toeither the open position or toward the open position to an intermediateposition, based on the exhaust gas pressure being above the thresholdexhaust gas pressure.

It is contemplated that the method 750 could be performed intandem/consecutively to the method 700, operation of the snowmobile 10could include implementations of both of the methods 700, 750.

It is contemplated that the method 750 could include additional ordifferent steps, either to perform additional functions and/or toperform the steps described above. It is also contemplated that thesteps described above could be performed in an assortment of differentsequences, depending on for example user preferences, and is not limitedto the order set forth in the explanation above.

Operation Based on Engine Speed and Throttle Position

In reference to FIG. 23 , another non-limiting implementation ofcontrolling operations in the exhaust system 600 is set out in the formof a method 800 for controlling the flow of exhaust gas from the engine26. The method 800 is performed by the system controller 500 accordingto the present technology. In some implementations, it is contemplatedthat an additional or substitute computational system could beimplemented to perform the method 800.

In addition to controlling the position of the valve 630 to manageintake and exhaust pressures based on environmental conditions (i.e.atmospheric pressure), the exhaust system 600 is further operable toadjust exhaust gas flow to balance providing additional boost whilelimiting backpressure when the user of the snowmobile 10 requestsadditional power from the snowmobile 10.

In one non-limiting scenario, the method 800 could be implemented in asituation where the throttle lever 86 is moved to make a high powerrequest to the engine 26, for example during acceleration of thesnowmobile 10. As will be outlined in the steps below, the valve 630 ismoved to the closed position, to spool up the turbocharger 300, inresponse to this movement of the throttle lever 86. With theturbocharger 300 in use, the engine 26 would then benefit from a denserintake air charge and would have increased power output compared to asimilar engine that would be naturally aspirated. As will further bedescribed below, requesting too much boost and directing all exhaust gasalong the turbine exhaust flow path 675 may also cause the backpressureto build beyond an optimized level to the desired engine operation. Insuch a situation, the method 800 can further move the valve 630 backtoward the open position in order to allow some exhaust gas to bypassthe exhaust turbine 350, thus decreasing the backpressure.

The method 800 begins at step 810 with determining, by the engine sensor586, the engine speed of the engine 26. The method 800 then continues,at step 820, with determining a throttle valve position of the throttlevalve 39 of the engine 26. The position of the throttle valve 39 issensed by the throttle valve position sensor 588, as is mentioned above.

In some implementations, step 820 could include determining a rate ofthrottle valve opening of the throttle valve 39 instead or in additionto determining the throttle valve position. The throttle valve positionsensor 588, alone or in conjunction with the system controller 500,could also be used to measure the rate of throttle valve opening in someimplementations. The steps 810, 820 may be performed in either order, orsimultaneously, depending on the specific implementation.

The method 800 then continues, at step 830, with moving the valve 630 tothe open position, the closed position, or any intermediate position,based on the engine speed and the throttle valve position determined insteps 810, 820, as well as the starting position of the valve 630. Inthe method 800, the throttle valve position is taken into considerationto assist in controlling the exhaust gas flow for managing operation ofthe engine 26.

In some implementations or iterations, the method 800 could furtherinclude moving the valve 630 based on a temperature of the exhaust pipe202, in addition to the engine speed and the throttle valve positiondetermined in steps 810, 820. The temperature of the exhaust pipe 202 isreceived by the system controller 500 from the temperature sensor 512.In some implementations, moving the valve 630 could be basedadditionally or alternatively on the temperature of the exhaust gaswithin the exhaust pipe 202, as sensed by the temperature sensor 512.

In some implementations, the method 800 could further includedetermining a pressure differential and further moving the valve 630based on the pressure differential. In some implementations, thepressure differential is determined by comparing a predetermined boostpressure of air flowing into the engine 26 against an actual boostpressure of air flowing into the engine 26. The predetermined boostpressure, described above in more detail, is determined based at leaston one of the throttle position and the engine speed, as determined insteps 810, 820 and corresponds to what the boost pressure should beflowing into the engine 26 based on the throttle position and/or theengine speed. The actual boost pressure of air flowing into the engine26 is determined by measuring the air intake pressure by the intakepressure sensor 504 and the system controller 500, as is describedabove. In some implementations, the actual boost pressure could bedetermined differently.

In some implementations, the method 800 could further includedetermining if the engine 26 is operating at a low altitude or a highaltitude (i.e. that the snowmobile 10 is being operated at low or highaltitude) prior to moving the valve 630. In some implementations,determining if the engine 26 is operating at low altitude or highaltitude includes determining an atmospheric pressure of air enteringthe snowmobile by the intake pressure sensor 504. It is alsocontemplated that the system controller 500 could include or becommunicatively connected to an altimeter or similar altitude measuringdevice.

Upon determining that the engine 26 is operating at low altitude, themethod 800 could then continue with retrieving a desired valve positionfor the valve 630 from a low altitude data set. Upon determining thatthe engine 26 is operating at high altitude, the method 800 could thensimilarly continue with retrieving the desired valve position for thevalve 630 from a high altitude data set. In some implementations, thelow altitude data set and the high altitude data set could be stored inthe storage medium 507 communicatively connected to or part of thesystem controller 500.

The desired valve position retrieved from the low or high data setsgenerally corresponds to an optimized or predetermined valve positionbased on the altitude and the engine speed and/or the throttle position,such that air flow into the engine 26 is matched to the operatingconditions of the engine 26. In such an implementation, havingdetermined a desired position of the valve 630, moving the valve 630 atstep 830 would be performed by moving the valve 630 to the desiredposition.

In some implementations or iterations, the method 800 could furtherinclude determining, based at least on the throttle position and theengine speed determined in steps 810, 820, a threshold pressuredifferential of the engine 26. The method 800 then continues withdetermining an actual pressure differential of the engine 26. In someimplementations, determining the actual pressure differential includesdetermining the exhaust pressure downstream of the engine 26 by theexhaust pressure sensor 590, determining the air intake pressureupstream of the engine 26 by the intake pressure sensor 504, anddetermining the difference thereof.

The method 800 then continues with determining that the actual pressuredifferential is greater than the threshold pressure differential andmoving the valve 630 toward the open position if the valve 630 is eitherclosed or an intermediate positions. In such a case, the actual pressuredifferential being greater than the threshold pressure differentialcould indicate that there is too much air pressure moving into theengine 26. This could have detrimental effects on operation of theengine 26, and the method 800 could thus provide correction by allowingmore exhaust gas to bypass the exhaust turbine 350 by further moving thevalve 630 toward the open position.

In some implementations or iterations, the method 800 could furtherinclude determining that an intake pressure, as determined by the intakepressure sensor 504, is above an intake threshold and determining thatthe throttle valve position is beyond a valve position threshold. Forinstance, the method 800 could determine that there is too much airpressure moving into the engine 26 while the throttle valve 39 has beenopened too far. This combination could have detrimental effects onoperation of the engine 26, and the method 800 could provide correctionby allowing more exhaust gas to bypass the exhaust turbine 350 byfurther moving the valve 630 toward the open position.

Based on the intake pressure and the throttle valve position being pasttheir respective thresholds, the valve 630, could then be moved fromclosed position or an intermediate position toward the open position.This allows for a decrease in backpressure induced by either too muchair intake or requesting too much throttle too quickly.

In some implementations or iterations, the method 800 could furtherinclude moving the valve 630 toward the closed position, subsequent tomoving the valve 630 toward the open position, such that a portion ofthe exhaust gas flowing through the exhaust turbine 350 of theturbocharger 300 is increased. In such implementations, the method 800provides some tuning of the exhaust gas flow to balance boost from theturbocharger 300 while limiting detrimental effects of increasedbackpressure, which assists in smoothing the power increase of theengine 26.

In some implementations or iterations, the method 800 could furtherinclude determining that the intake pressure is above the air intakepressure threshold, subsequent to moving the valve toward the closedposition. The method 800 could then include moving the valve 630 towardthe open position, based on the intake pressure being above thethreshold.

In some implementations or iterations, the method 800 could furtherinclude determining that the intake pressure is below the intakepressure threshold subsequent to moving the valve toward the closedposition. The method 800 could then further include moving the valve 630further toward the closed position, in order to allow further boost fromthe turbocharger 300.

In some implementations, the determining the intake air pressure couldinclude determining the intake pressure at a location downstream of theturbocharger 300 by a pressure sensor (not shown). Moving the valvecould then include selectively moving the valve based on the intakepressure determined by the pressure sensor downstream from theturbocharger 300.

In some implementations, the method 800 could further includedetermining the exhaust pressure downstream of the engine 26 by theexhaust pressure sensor 590 and moving the valve 630 toward the openposition based on the exhaust pressure being above a predeterminedexhaust pressure threshold.

In some implementations, where the rate of throttle valve opening isdetermined, the method 800 could further include determining that therate of throttle valve opening is above a threshold rate; and moving thevalve 630 toward the open position based at least on the rate ofthrottle valve opening being above the threshold rate. In such animplementation, the valve 630 is opened up, for example, when too muchthrottle is requested too quickly, in order to prevent backpressure fromhaving a detrimental effect on engine operation (especially when theuser is trying to increase power from the engine 26). In someimplementations, the method 800 could further include determining thatthe intake pressure is above the threshold intake pressure and movingthe valve 630 based on both the rate of throttle valve opening beingabove the threshold rate and the intake pressure being above thethreshold intake pressure.

It is contemplated that the method 800 could include additional ordifferent steps, either to perform additional functions and/or toperform the steps described above. It is also contemplated that thesteps described above could be performed in an assortment of differentsequences, depending on for example user preferences, and is not limitedto the order set forth in the explanation above.

As described above, various methods of controlling operation of theturbocharger 300 involve monitoring the backpressure affecting theengine 26. In view of the availability of the pressure information inthe present technology, operation of the snowmobile 10 can further beoptimized by making adjustments to the fuel-air mixture in the engine26.

Changes in the backpressure in the engine 26 and the exhaust system 600impacts the fuel to air ratio present in the engine 26. All other thingsremaining equal, the engine 26 obtains maximum power when a targetbackpressure is maintained. If the effective backpressure in the engine26 deviates from that target, the fuel to air ratio is affected, whichin turns diminishes the operation of the engine 26.

With increasing backpressure, the total amount of air flowing throughthe engine 26 is reduced. In such a circumstance, a constant amount offuel injected would cause an increased fuel to air ratio in the engine26 and as such the engine 26 would be provided with a fuel-air mixturethat is too rich. As such, the engine 26 may not perform optimally.

Too much of a decrease in backpressure at high engine speed, all otherthings being equal, would also lead to an increase in the fuel to airratio. When backpressure is too low, pressure waves created by theexhaust pipe 202 (which aid creating a trapping effect to maintain airin a two-stroke engine) could be mistimed, and the combustion chambersof the engine 26 are emptied of more air than optimally would occur. Insuch a case, the engine 26 would again end up with a richer fuel-airmixture (receiving the same amount of fuel with less air). Once againthe engine 26 may not perform optimally.

Supplying a Fuel-Air Mixture

With reference to FIGS. 24 and 33 , a method 900 of supplying a fuel-airmixture in the engine 26 of the snowmobile 10 will now be described.

The method 900 begins with at step 910 with determining a pressuredifferential between an intake air pressure of air flowing toward theengine 26 and an exhaust gas pressure of exhaust gas flowing out of theengine 26. This pressure differential, as mentioned above with respectto the dynamic regime, generally correlates with the backpressure in theengine 26. The pressure differential is determined by comparing, by thesystem controller 500, measurements taken from the air intake pressuresensor 504 and the exhaust pressure sensor 590. In some implementations,it is contemplated that the snowmobile 10 could include a differentialsensor for determining the pressure differential in a singlemeasurement.

In some implementations of the method 900, the pressure differential isdetermined in two steps. Specifically, by determining the intake airpressure, by the air intake pressure sensor 504, at sub-step 912. Thenthe method 900 continues with determining the exhaust gas pressure, bythe exhaust pressure sensor 590, at sub-step 914. Depending on thespecific implementation, the steps 912, 914 could be performed in anyorder, or simultaneously.

The method 900 continues, at step 920, with determining an amount offuel to be injected into the engine 26 based on at least the pressuredifferential (as determined in step 910). The system controller 500calculates the amount of fuel to be injected, such that the fuel-airmixture is maintained at an appropriate value, based at least on thebackpressure in the engine 26. It is contemplated that another computingsystem could be included to manage the determination of the amount offuel to be injected, rather than the system controller 500. A base fuelinjection quantity is determined by using a dataset relating an amountof fuel to be injected corresponding to the current TPS and RPM. Anexample base fuel injection dataset 982 is shown in FIG. 34 where thebase fuel injection is indicated as a volume, in this example in mm³.

In some implementations, the base fuel injection quantity could bemodified according to the backpressure as follows. A target backpressure (the exhaust pressure less the intake pressure) is determinedfrom a dataset of TPS and RPM, such as in the example dataset 984. Theactual back pressure is obtained from the exhaust pressure minus theintake pressure using the exhaust pressure sensor 590 and the intakepressure sensor 504 respectively.

A fuel correction quantity or percentage would then be obtained from afuel correction dataset 986 of RPM and the difference between the actualbackpressure and the target backpressure (identified as ΔΔP). The fuelcorrection from this dataset 986 would then be applied to the base fuelinjection quantity to determine a final injection quantity, modifiedaccording to the measured backpressure.

The method 900 then terminates, at step 930, with injecting the amountof fuel (as determined in step 920) into the engine 26. The fuel isinjected by the fuel injectors 41, as is described above.

It is contemplated that in some implementations, the method 900 couldrecommence after step 930. In some implementations, the method 900 couldcontinue beyond step 930 with determining a changed pressuredifferential. The method 900 could then continue with determining arevised amount of fuel based on the changed pressure differential. Thisimplementation of the method 900 could then terminate with injecting therevised amount of fuel into the engine 26.

In some implementations, the method 900 could include determining thatthe pressure differential has increased, determining a reduced amount offuel to be injected, and injecting the reduced amount of fuel into theengine 26. In some implementations, the method 900 could also includedetermining that the pressure differential has decreased, determining areduced amount of fuel to be injected, and injecting the reduced amountof fuel into the engine 26.

In some implementations, the method 900 repeats following step 930, atsome predetermined time interval, to readjust the fuel-air mixture inorder to compensate for changes in the backpressure. In someimplementations, the method 900 could be performed by the systemcontroller 500 intermittently during operation of the snowmobile 10. Itis also contemplated that that method 900 could be performed only onceor only a few times during operation of the snowmobile. It is furthercontemplated that the method 900 could be performed in response to thepressure differential and/or the intake or exhaust pressures passing apredetermined threshold.

In some implementations, the method 900 could further includedetermining the engine speed, and the determining the amount of fuel tobe injected is also based on the engine speed. In some implementations,the method 900 could further include determining the throttle positionof the throttle valve 39, and the determining the amount of fuel to beinjected is further based on the throttle position.

It is further contemplated that additional variables could be taken intoaccount when determining or calculating the amount of fuel to beinjected, in addition to the pressure differential. These could include,but are not limited to: engine speed (rpm), the throttle position, theair temperature, ambient barometric pressure, close loop wide bandlambda control, and temperature of the exhaust gas.

It is contemplated that the method 900 could include additional ordifferent steps, either to perform additional functions and/or toperform the steps described above. It is also contemplated that thesteps could be performed in an assortment of different sequences,depending on the specific implementation.

Modifications and improvements to the above-described implementations ofthe present technology may become apparent to those skilled in the art.The foregoing description is intended to be exemplary rather thanlimiting. The scope of the present technology is therefore intended tobe limited solely by the scope of the appended claims.

What is claimed is:
 1. A valve for use in an engine exhaust conduit,comprising: a base portion configured for pivotably mounting the valvewithin the engine exhaust conduit, the base portion defining a valvepivot axis, the valve being pivotable about the valve pivot axis duringuse; and a body portion extending from the base portion, the bodyportion having an upstream side and a downstream side opposite theupstream side, the upstream side being exposed, during use, to fluidflow in the engine exhaust conduit, the body portion having a generallypointed shape defining a rounded tip at a location of the body portionfurthest from the base portion in a length direction of the valve, thelength direction of the valve being generally perpendicular to the valvepivot axis, the body portion having a periphery including: two oppositelengthwise edges extending from the base portion in a directiongenerally parallel to the length direction of the valve; a rounded edgedefined by the rounded tip; and two converging angular edges extendingbetween the two lengthwise edges and ends of the rounded edge, the twoangular edges converging toward each other as the two angular edgesextend from the two lengthwise edges to the ends of the rounded edge, atleast a portion of each of the two converging angular edges beingsubstantially straight.
 2. The valve of claim 1, wherein each of the twoangular edges is disposed at an angle between 10° and 45° inclusivelyrelative to the length direction of the valve.
 3. The valve of claim 1,wherein the body portion of the valve is symmetrical about a planebisecting the rounded tip, the plane being perpendicular to the valvepivot axis.
 4. The valve of claim 1, wherein: the body portion has awidth measured in a direction parallel to the valve pivot axis; and thewidth of the body portion is largest adjacent the base portion andsmallest at the rounded tip.
 5. The valve of claim 4, wherein: the valvehas a length measured from the base portion to the rounded tip in thelength direction; and a ratio of the length of the valve over a maximalwidth of the body portion is greater than
 1. 6. The valve of claim 4,wherein: the rounded tip has a tip radius; and a ratio of a maximalwidth of the body portion over the tip radius is greater than
 2. 7. Thevalve of claim 1, wherein the body portion comprises a ridge disposed onthe upstream side, the ridge forming a closed shape.
 8. The valve ofclaim 7, wherein a cross-sectional profile of the ridge is generallytrapezoidal.
 9. The valve of claim 1, wherein the body portion comprisesa peripheral lip protruding on the downstream side.
 10. The valve ofclaim 1, wherein the base portion and the body portion are madeintegrally such that the valve is a single-piece component.
 11. Thevalve of claim 1, wherein each of the two converging angular edges issubstantially straight.
 12. The valve of claim 1, wherein a planecontaining the valve pivot axis extends along the body portion of thevalve.
 13. A turbocharger system for an internal combustion engine,comprising: a turbocharger for compressing and feeding air to theengine, the turbocharger having a turbine; a bypass conduit in fluidcommunication with the engine and the turbocharger, the bypass conduitbeing configured to selectively direct exhaust gas to the turbochargerfor operating the turbine or to bypass the turbine, the bypass conduitcomprising a valve seat defining a valve opening; a valve disposed inthe bypass conduit for controlling exhaust gas flow through the valveopening, the valve comprising: a base portion pivotably mounted withinthe bypass conduit at the valve seat, the base portion defining a valvepivot axis, the valve being pivotable about the valve pivot axis; and abody portion extending from the base portion, the body portion having anupstream side and a downstream side opposite the upstream side, theupstream side being exposed, during use, to exhaust gas flow in thebypass conduit, the body portion having a generally pointed shapedefining a rounded tip at a location of the body portion furthest fromthe base portion in a length direction of the valve, the lengthdirection of the valve being generally perpendicular to the valve pivotaxis, the body portion having a periphery including: two oppositelengthwise edges extending from the base portion in a directiongenerally parallel to the length direction of the valve; a rounded edgedefined by the rounded tip; and two converging angular edges extendingbetween the two lengthwise edges and ends of the rounded edge, the twoangular edges converging toward each other as the two angular edgesextend from the two lengthwise edges to the ends of the rounded edge, atleast a portion of each of the two converging angular edges beingsubstantially straight; a valve actuator operatively connected to thebase portion of the valve, the valve actuator being operable to causethe valve to pivot about the valve pivot axis; and a controller incommunication with the valve actuator for controlling operation of thevalve actuator for controlling a position of the valve.
 14. Theturbocharger system of claim 13, wherein the valve seat has a shapematching the shape of the body portion of the valve.
 15. Theturbocharger system of claim 13, wherein the valve is movable by thevalve actuator between a plurality of positions including: an openposition in which exhaust gas flow through the valve opening issubstantially unimpeded by the valve; a closed position in which thevalve fully closes the valve opening such that exhaust gas flow throughthe valve opening is cut off by the valve; and a plurality ofintermediate positions between the open position and the closedposition.
 16. The turbocharger system of claim 15, wherein: the bodyportion comprises a ridge disposed on the upstream side, the ridgeforming a closed shape; and in the closed position of the valve, theridge sits against the valve seat.
 17. The turbocharger system of claim13, wherein the valve actuator is a servomotor.
 18. The turbochargersystem of claim 13, wherein the valve is oriented in the bypass conduitsuch that the rounded tip of the body portion is downstream of the baseportion of the valve.
 19. The turbocharger system of claim 13, wherein:the bypass conduit comprises: a turbine outlet portion for directingexhaust gas flow to the turbocharger; and a bypass outlet portion fordirecting exhaust gas flow away from the turbocharger; and the valveseat and the valve are disposed in the bypass outlet portion to controlexhaust gas flow into the bypass outlet portion.
 20. The turbochargersystem of claim 13, wherein a plane containing the valve pivot axisextends along the body portion of the valve.